1. Field of the Invention
The present invention relates to an electrostatic comb actuator in a MEMS field or the like, and more particularly, to an electrostatic comb actuator that is applicable to, for example, a deformable mirror. Moreover, the present invention relates to an adaptive optics system using the deformable mirror, and a scanning laser ophthalmoscope using the adaptive optics system.
2. Description of the Related Art
An electrostatic comb actuator is one of drive units having a fine mechanical structure, and can perform micro-driving in accordance with a potential difference between comb electrodes. Further, the electrostatic comb actuator is also applicable to sensing by measuring the change in distance between comb teeth, which is caused by external factors, as a change in electrostatic capacitance. The electrostatic comb actuator can thus be used as a micro-driving unit and a sensor structure, and hence is expected to be applied as a structure capable of realizing downsizing and integration of an element in technical fields such as information and communication, medical care and biotechnology, automobiles, and robots.
A general electrostatic comb actuator is next described. Japanese Patent Application Laid-Open No. 2010-008613 proposes an electrostatic comb actuator structure in which a movable comb electrode, a fixed comb electrode, and an elastic body are formed in a device layer of a semiconductor substrate, and a separation groove for the electrodes is formed in a handle layer of the semiconductor substrate.
Japanese Patent Application Laid-Open No. 2010-008613 discloses that a movable comb electrode, a fixed comb electrode, and a beam (hinge) are made up of a device layer of an SOI substrate (semiconductor substrate), which has a thickness of, for example, about 30 μm. The electrostatic comb actuator is configured to rotate a movable portion about an axis formed by the beam. Considering application of the above-mentioned configuration to a configuration for displacing the movable portion in a direction perpendicular to the substrate, in order to increase the displacement amount of the movable portion, the beam needs to be thinned. However, in this case, when the beam is thinned, the comb electrodes are also thinned. As a result, sufficient displacement amount may not be obtained. Further, in the configuration disclosed in Japanese Patent Application Laid-Open No. 2010-008613, a handle layer separation groove is formed as the electrode separation groove, and a connection portion in the separation groove is made up of a silicon device layer which has a thickness of, for example, about 30 μm. However, considering the above-mentioned configuration, thinning the beam results in reduction in strength of the connection portion.